The effects of visual deprivation on the formation of retino-geniculate synapses will be studied quantitatively with the electron microscope. Cats will be deprived by eyelid suture at the time of normal eye opening and allowed to survive for periods of time ranging from 2 to 32 weeks. Sections from normal and deprived layers of the lateral geniculate nucleus will be examined to determine the rate at which synapses from the retina are formed as well as the details of synaptic organization. These results will be compared with those from normal cats to determine if deprivation affects either the development of retinogeniculate synapses or the maturational endpoint of the system.